Telephone system



Sept. 8, 1942. J. H. voss' TELEPHONE SYSTEM 2 Sheets-Sheet 1 Filed Aug.3, 1940 Qm. hm

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INVENTOR .JOHN H. v'oss ATTORNEYS sept. s, 1942.

4. H. voss TELEPHONE SYSTEM Filed Apg, 3, 1940` 2 sheets-sheet 2 w w ..wMSS mmw m SS m@ lNvENToR JOHN H. Voss ATTORNEYS Patented Sept. 8, 1942UNITED STTES PTENT FFICE TELEPHONE SYSTEM Application August 3, 1940,Serial No. 350,465

15 Claims.

The present invention relates to telephone systems and more particularlyto improvements in trunk circuit apparatus of the character utilized interminating inter-exchange trunks in an exchange of the automatic type.

In small community automatic exchanges, commonly known as C. A. Xs, thecharacter of the automatic switching equipment is frequently such thatthe outlet contacts of the iinder and connector switches utilized arearranged in sets for subscriber line termination, and the correspondingcontacts of the contact sets having the same directory numberdesignations are conductively connected together. This line multiplearrangement, wherein the private or control contacts as well as thetalking contacts of the corresponding contact sets are conductivelyconnected, is known as a straight multiple. While this type of outletcontact multiple is entirely adaptable to subscriber line termination,it is not Well adapted for use in conjunction with the conventionaltrunk circuits now used to terminate inter-exchange trunks. Morespecically, conventional trunk circuit arrangements require, for properoperation, a separation of the control leads eX- tending to the nderswitches from the control leads extending to the connector switches.

It is an object of the present invention, therefore, to provide in asystem of the character described, an improved trunk circuit, which isso arranged that it may be directly substituted for a subscriber linecircuit without in any way altering the multiple wiring of the finderand connector switches or the equipment common to these switches.

It is another object of the invention to provide an improved trunkcircuit of the character noted, which is equipped to provide supervisoryand trunk lockout facilities, and is extremely simple in arrangement.

It is a further object of the invention to provide in a telephone systemof the character described, an improved trunk circuit arrangementwherein two trunk circuits, each adapted for use with trunks individualthereto, are cooperatively used in conjunction with a single trunk andtwo 'sets of outlet contacts of the associated finder and connectorswitches, so that the trunk may be seized by a connector switch as afirst choice trunk for one type of call and as a second choice trunk foranother type of call.

In the illustrated embodiment of the invention there is provided a smallcommunity exchange which is connected with a central exchange of themanual type by means of inter-oice trunks of two types, namely, toll andfree service trunks.V

The community exchange is of the automatic type, finder-connector linksand common equipment including a link distributor being provided thereinfor setting up connections between the lines terminating at theexchange. Straight line multiples between the outlet contacts of thelink nder and connector switches are used, so that a subscriber lineconnection may be made by connecting the subscriber line equipment, i.e., the line, cut-off and lockout relays directly to the private andtalking leads of a particular multiple having the desired directorynumber designation. Each of the trunks utilized solely for toll serviceand free service are terminated in the C. A. X in trunk circuitsindividual thereto, these trunk circuits being so connected and arrangedthat they may be directly connected to a subscriber line multipleindividual thereto. Each of these trunk circuits is so connected andarranged that by disconnecting a set of subscriber line relay equipmentfrom a line multiple the talking and private leads of the trunk circuitmay be directly connected to the talking and private leads of theselected multiple. These trunk circuits individually comprise line,lockout and cut-off relays which are so arranged that the associatedtrunk is locked out of service when a permanent calling condition existsthereon. Each trunk circuit further includes a supervisory relay whichis controllable over the private lead of an associated line multiple totransmit on-hook and oi-hock supervisory signals over the associatedtrunk through the expedient of reversely connecting the talkingconductors of the associated trunk to the talking conductors of theassociated line multiple.

One of the trunks connecting the C. A. X with the manual oince is usedas a combination toll and free service trunk. More specically, thistrunk is normally used as a iirst choice, free service trunk, butprovisions are made whereby it may be used as a second choice toll trunkon calls routed from the substations served by the C. A. X to thecentral exchange. The provisions whereby these combined servicefacilities are obtained include a combination of two of the trunkcircuits normally used for individual trunk termination. Morespecifically, the switchboard trunk sections of these two trunk circuitsare individually connected to line multiples having different directorynumber designations, one of these designations representing the rstchoice free service directory number, and the other designationrepresenting the second choice toll trunk designation. Both of the twotrunk circuits are equipped with line, cut-off, lockout and supervisoryrelays, whereby the facilities mentioned above are provided regardlessof which trunk circuit is taken for use in seizing the singleassociatedtrunk. In addition, provisions are made in the circuit arrangementformed by the combination of the two trunk circuits, whereby when eithertrunk circuit is seized the other trunk circuit is marked againstseizure. Provisions are also made for selectively switching theassociated inter-office trunk between the two trunk circuits, dependingupon the type of call being handled.

The novel features believed to be characteristic of the invention areset forth with particularity in the appended claims. to its organizationand method of operation, together with further objects and advantagesthereof, will best be understood by reference to the specification takenin connection with the accompanying drawings, in which Figures 1 and 2,considered together, illustrate a telephone system havingincorporatedtherein the features oi' the 'invention as briefly outlinedabove.

Referring now more particularly to the drawings the system thereillustrated comprises a manual oiicev 5 and a C. A. X I0, each of whichis arranged for subscriber line termination. These two exchangesA areinter-connected by means of a group of toll trunks including the trunkandV a-group of free service trunks. An additional trunkA 9| is providedwhich, in the arrangement illustrated, is utilized as a rst choice freeservice trunk and 'as a second class toll trunk. These trunks terminatein the central exchange at different operators positions of an operatorsswitchboard 6 which may be entirely conventional in arrangement.

The automatic switching apparatus provided in the C. A. X I0 ispreferably of the character disclosedand claimed in applicants copendingapplication, Serial No. 189,121, filed February '7, 1938. -Brieflydescribed, this apparatus comprises a plurality of finder-connectorlinks, one of which is indicated at I5 as including the nder switch 25and the connector switch 30, and common equipment 20. The finder andconnector switches are of the all-relay type, group and unit relaysarranged in a novel manner being Vprovided in each switch for performing.the required lineselecting functions.. Each of the finder switches isfully selective in character, auxiliary group and unit :relays beingprovided in the common equipment20 for causing the instantaneousoperation of the corresponding relays in anassigned nder switch inresponse ,to the initiation of a call on oneof the lines accessible tothe links. The links are successively assigned for use in apredetermined order through the provision of a link distributor which isalso of the all-relay type. Straightline multiples are utilized toconnect the corresponding contacts of the link finder and connectorswitches. Thus, the outlet contacts formingthe ,contact set IIf of thefinder switch 25 are conductively connected by means of two talkingleads and a private lead directly to the outlet contacts formingthecontact set ||c of the connector switch 3.0. This multiple is alsoextended to the contact sets having the directory number. designation XIIX of the other link nder and connector switches. In a similar manner,the nder outlet contacts .0If are directly multipled to the connectoroutlet contacts 0| c; the finder outlet contacts 02 f are .directlymultipled to the connector outlet contacts 020; and the The invention,both as Vtion of the two trunk circuits.

iinder outlet contacts 9|, are directly multipled to the connectoroutlet contacts 9|c. These line multiples are carried to a distributingframe at which connections are made to the subscriber line equipment.Thus, the line circuit I2, which is provided in association with thesubscriber line II serving the substation A, may be connected to theline multiple having any desired directory number designation by makingthree connections at the distributing frame. In the arrangementillustrated, this line circuit is connected to the line multiple havingthe directory number designation XI IX.

Each of the inner-ofce trunks inter-connecting the C. A. X I0 and thecentral exchange 5 is terminated in a trunk circuit which is connectedand arranged in accordance with the present invention. Thus, the tolltrunk 0| extends to a trunk circuit 35 having a trunk section which isconnected to the outlet contact multiple having the directory numberdesignation 0|. The arrangement of the trunk circuit 35 is identicalwith the arrangement of the trunk circuit 40,

which may either be used to terminate a second toll trunk 02 illustratedin dotted lines, or may be used in conjunction with the trunk circuit 45to terminate the combination toll and free service trunk 9|. Each of thetrunk circuits which terminates a toll or free service trunk individualthereto is identical in arrangement with the trunk circuit 40. Brieflydescribed, this trunk circuit comprises a line relay RI 0, a cut-01Trelay R|20, a slow-acting lockout relay R|00, a supervisory relay R|30and circuit connections therebetween which are described more fully inthe following portion of the specification dealing with the operation ofthe system. The trunk circuit 45 is substantially similar in arrangementwith the trunk circuit 40. More specifically, the trunk circuit 45comprises a line relay R2|0, a cut-olf relay R220, a lockout relay R200of the slow-acting type, a supervisory relay R230, a line-,switchingrelay R240 and a guard control relay R250. The two last-mentioned relaysare provided for the purpose of correlating the opera- In this regard itwill be noted that the trunk 9| may be seized through the trunk circuit45 directly over the trunk section |56 having the directory numberdesignation 9|, or may be seized through the trunk circuit 40 over thetrunk section |49 having the directory number designation 02. If morethan one toll trunk is required between the central exchange 5 and theC. A. X |0, the switchboard side of the trunk circuit 40 is connected tothe outlet contact multiple having the largest directory number. Thus,if three such trunks, in addition to a combination trunk, are required,the associated trunk circuits are connected-to the line multiples havingthe directory number designations 0I, 02 and 03, and the trunk circuit40 is connected to the line multiple having the directory numberdesignation 04. In any case where more than one toll trunk is provided,it is necessary to make provisions for automatic trunk selection. Tothis end there is associated with the finder-connector links of the C.A. X I0 a set of trunk preselect relays 50 which are of the characterdisclosed in Figs. 11 and 13 of the abovementioned copending applicationSerial No. 189,-

121 now U. S. Patent 2,252,309, granted August 12, 1941. Brieflydescribed, these relays are so arranged that when the first trunk of agroup, such, for example, as the trunk 0|, becomes busy, it is marked asbusy in all of the finder and connector switches, and the second trunk,namely, the trunk 02, is immediately allotted for use. If the secondtrunk is also busy at the time the first trunk is taken for use, thethird trunk, if idle, is allotted for use. Further, the arrangement ofthis relay group is such that the trunk having the lowest directorynumber designation is assigned for use in preference to the othertrunks. so long as it is not occupied with a call.

The operation of the trunk circuits 35, 4|), etc., individuallyterminating the toll and free service trunks, in handling calls incomingto the C. A. X I0, may best be understood by considering the trunkcircuit 40 as being used to terminate the toll trunk 02. In such case,the conductors C2 I5,

C2|6, C2I'| and C2I8 are disconnected from the terminals |68, |09, II'|and II 8, respectively, the talking conductors of the toll trunk |32 areconnected to the terminals .|28 and lili), and the terminals II'| andIIB are strapped or otherwise conductively connected. With this wiringarrangement, if one of the operators attending the switchboard 6 insertsthe calling plug of one of her cord circuits in the jack terminating thetoll trunk U2, a direct current path is bridged across the talkingconductors of this trunk to complete a circuit including the conductorsCI I5 and CI I6, and the contacts |2| and |25 for energizing the linerelay Rim). In operating7 the relay RII!! closes its contacts I I I toprepare a locking circuit for the lockout relay R509, and moves itscontacts I|2 out of engagement to open apoint in the operating circuitfor the supervisory relay RISO, At its contacts H3, the relay RIIGcompletes an obvious path for impressing ground potential upon the groupselect lead CIM. At its contacts I I4, the relay RI I connects the unitselect lead CIB? through the contacts to the start lead C208. When thegroup select lead CIBG is grounded, and the leads CID? and C228 areconnected together, the auxiliary relays of the common equipment 213operate to cause the operation of the corresponding relays in the finderswitch of the assigned link. Assuming that the link I5 is assigned tohandle the call,

the tenth group relay and the second unit relay of the finder switchoperate to extend a connection from the trunk section |59 to theconnector portion of the link. Incident to the operation of the relayequipment embodied in the f finder switch 25, a circuit is completed forenergizing the line relay of the connector switch 3Q, whereby the line,hold and impulse-correcting relays of this connector switch are causedto operate. mentarily to impress ground potential upon the conductorCIE!! and to impress ground potential upon the control conductor Ci52for the duration of the call. When the control Aconductor C!.52 isgrounded, the trunk preselect relays 553 operate to mark the trunk 02against seizure in all of the link connector switches. When the positivetalking conductor Cl! is grounded, a circuit including the contacts |32and i213 is coinpleted for energizing the upper winding of the cut-offrelay RIZG. The relay R522 now operates and locks to ground over a pathincluding the contacts |23 and |35, the strapped terminals EI? and IIB,and the grounded conductor CI52. After this locking circuit iscompleted, the relay RI20 opens its operating circuit at the contacts|24. At its contacts |26, the relay R422 completes an obvious circuitfor energizing the slowacting lockout relay RIii, At its contacts |21,the relay RIZU opens another point in the oper- These relays, inoperating, function moating circuit for the supervisory relay RI30. At

its contacts |2| and |25, the relay Rl2ll opens two points in theabove-traced operating circuit for the line relay RIIiI and, in sodoing, clearsV the trunk G2 of the impedance represented by the windingsof theA line relay. At its contacts |22, the relay RIZ extends thecalling loop through the contacts |32 and |37, and the contacts of theoperated relays in the finder switch 25 to the connector portion of thelink I5, thus establishing a pulsing circuit for the line relay of theconnector switch 3l).

The line relay RI I0, upon restoring, closes its contacts II2 toreprepare the operating circuit for the supervisory relay RI3S, andopens its contacts I I3 to disconnect the group select lead CIUB fromground. At its contacts II I, the relay RI I0 opens a point in thelocking circuit for the lockout relay Rlilil. At its contacts IIll, therelay RI Il) disconnects the units select lead CIIl'l from the startlead C298. The lockout relay Rlll, upon operating, prepares its lockingcircuit at the contacts IBI, and closes its contacts |02 to prepareanother path for impressing ground potential upon the control conductorCI52. At its contacts |93, the relay RIM opens another point in theoperating circuit for the supervisory relay RIBB. At its contacts |04,the relay RIDE) opens another point in the path for grounding the groupselect lead Clil. At its contacts H35y the relay Rieti opens a furtherpoint in the path for connecting the units select lead Cl'l to the startlead C298.

When the units select lead CIM is disconnected from the start lead C208,and the group select lead CIli is disconnected from ground, the operatedauxiliary relays embodied in the common equipment 2B are deenergized andrestore, Incident to the operation of the relay equipment embodied inthe link I5, the link distributor relays forming a part of the commonequipment 20 are caused to operate to select another idle link, and thelink I5 is marked against seizure. Thus, the common equipment 20 isfreed for use in handling another call which may be waiting or which maybe subsequently initiated.

Following the extension of the connection to the connector portion ofthe link I5 in the manner explained above, the operator handling thecall at the operators switchboard 6 in the central exchange 5, mayextend the connection to the desired line, and cause ringing current ofthe frequency or code designating the desired substation to be projectedover this line by dialing a four digit directory number. The rst digitis utilized to determine the type of ringing to be employed in signalingover the called line, i. e., bridged or divided ringing and partially toselect the ringing code or frequency of the ringing current. The seconddigit is utilized for the purpose of causing the operation of theconnector group relay which terminates the group of ten lines includingthe called line. Thus, if the substation A, served by the line II, iscalled, the dialing of the second digit will result in the operation ofthe first group relay of the connector switch 30. The third digit dialedat the calling operatcrs position 6 in the manual exchange 5 is utilizedfor the purpose of causing the operation of the connector unit relayswhich correspond to the particular desired line. In the case underconsideration, the first unit relay of the connector switch 3G will beoperated in response to the dialing of the third digit. The fourth digitdialed is used to complete the selection of the particular 'code or-frequency of the ringing current to be projected over the selected lineII. Immediately after the called line II is selected it is tested todetermine the idle or busy condition thereof. In the event the line isbusy, the usual busy tone signal is transmitted over the trunk 02 toinform the calling operator that the desired connection cannot beobtained, and the ringing circuits are held open to prevent thetransmission of ringing current over the selected line. AOn the otherhand, if the called line is idle, ringing current of the selected codeor frequency i-s projected thereover for the purpose of energizing fvided at certain of the other substations served by this line but thecoded character of the signals produced indicates that only thesubstation A is being called. The desired conversational circuit isestablished when the call is answered at the called substation A. Inresponse to this operation, the back-bridge relay embodied in theconnector switch 3i) operates to reverse the direction of current flowover the conductors of the trunk 92 in the usual manner. This currentreversal causes the operation of a polarized supervisory relay embodiedin the trunk circuit terminating the toll trunk 02 at the operatorsswitchboard 6, whereby an oit-hook supervisory signal is produced at thecalling operators position of this switchboard, indicating that the callhas been answered. The back-bridge relay of the connector switch 30 alsofollows the connection release and the call answering operations whichmay subsequently be performed by manipulation of the switchhook providedat the substation A, so that the usual` flashing recall and disconnectsignals are produced by the supervisory lamp associated with theconnection at the calling operators position in the central exchange 5.Thus, the operator handling the call may be informed that she is beingrecalled by the calledparty and is also informed when the connection isreleased at the called substation. The release of `the connection isentirely under the control of the operator handling the callv at theswitchboard 6 in the central exchange 5. More specifically, when adisconnect or on-hook supervisory signal is transmitted to the callingoperator, indicating that the connection has been releasedl at thecalled substation, the operator may initiate the release of the Iswitchtrain by withdrawing the calling plug of the cord circuit included inthe connection from the jack termiu nating the trunk 02. In response tothis operation, the loop circuit extending from the calling operatorsposition to the connector switch 3D is interrupted to cause thedeenergization and release of the line and hold relays embodied in thisswitch. When the hold relay of the connector switch 3Q restores, thefinder and connector switches 25 and 30, respectively, andthe linecircuit I2 are restored to normal in the manner explained in detail inthe above-mentioned copending application. During the release of thelink I5, the link is marked as idle in the distributor relays of thecommon equipment 2li, and ground potential is removed from the controlconductor CI 52 of the trunk section M9. When this control conductor isdisconnected from ground, the cutoff relay RIZ() is deenergized andrestores to open,

fat its contactsll26, the operating circuit for thev i. lockout relayRfIlJII.- Following therelease of fthe lockout relay R100, vthetrunk'circuit 40 is fully energized and restores.

f restored to normal Aand is marked as idle in the trunk preselectrelaygroup 50.

As indicated in the introductory portion of the specication, provisionsare kmade in the trunk circuit 4U for locking this-circuit and theassociated trunk 02, if used, out of servicev when a permanent callingconditionoccasioned by a fault or the like is present on this trunk.Under these circumstances, the link I5, for example, may be seized inthe manner explained above, but, following seizure thereof, no dial'pulses are transmitted to the connector switch 30. When the link I5 isseized, a timing ldevice common to the links of the exchange isconditioned forcibly to release the link after the expiration' of apredetermined time interval in Ithe event a talking circuit is notestablished by Way of :the link before the predetermined time intervalexpires. Should this contingency be met', the control equipment of thelink I5, in releasing,` disconnects the control conductor CI 52 fromground, whereby the operated cut-oi relay-RIZ!) is de- This relay, inreleasing, reconnects the windings of the line relay RIIU to theconductors of the trunk 02 upon which the calling condition is stillpresent. Accordingly, the line relay RI I0 reoperates to complete, atits contacts III, the prepared locking circuit for the still operatedlockout relay RI I!J. Thus, the line and lockout relays R'I I0 and Rll),respectively, are locked energized. With the vrelay Ri operated, and thecut-off` relay R'I2 in its restored position, an auxiliary path,vincluding the contacts |32 and I2'I is completed-for maintaining groundpotential upon the control conductor CI52; whereby the trunkcircuitfsdll is guarded against seizure by one of the connector switchesprovided in the C. A. X; With the lockout relay RIQO operated, the startcircuits described above, and including the group select lead CIBG, theunits select lead CI'I and the start lead CIIIS, are held open toprevent the finder portion of an assigned link from operating to seizethe trunk section M9. It will be `obvious that the two relays RIIU andVRlll remain in their respective operated positions until the permanentcalling condition present on `the toll trunk 02 is cleared. When thefault responsible for this condition is corrected, the line relay RI I0is deenergized and restores to cause the release of the lockout relay Rlin an obvious manner. With these two relays restored, the trunk circuit40 is fully released, and this circuit is `marked 5as idle in the relaysof the trunk preseiect group The manner in which the trunk circuit- 45operates in the extension of a call from the' operators switchboard 6 byWay of the' trunk 9| and the link I5, for example, to the subscriberAline II, for example, is substantially similar to the mode of operationof the trunk circuit' SE1 as described above. In this regard it will beunderstood from the preceding explanation that 'the trunk circuit 45 isin all cases used in conjunction with the trunk circuit 4@ or theequivalent thereof, and terminates a combination toll'and free servicetrunk. More specifically, if one of the operators having access to thetrunk 9| at the operators switchboard 6 inserts the calling plug of oneof her cord circuits in the jack terminating the conductors of thistrunk to establish a direct current path between the talking conductorsof the trunk, the line relay R2 I is energized and operates. Uponoperating, the relay R2|0 closes its contacts 2|3 to impress groundpotential upon the group select lead C200, and closes its contacts 2|4to connect the units select lead C201 to the start lead C208. Inresponse to these operations, the finder portion of the assigned link,such, for example, as the link l5, is caused to operate to seize thetrunk circuit 45 over the trunk section |56 in the manner describedabove. 'I'he line relay R2|0, in operating, also opens, at its contacts2|2, a point in the operating circuit for the supervisory relay R230. Atits contacts 2||, the relay R2|0 completes an obvious circuit forenergizing the guard control relay R250. The relay R250, upon operating,closes its contacts 252 to complete an obvious path for impressingground potential upon the connected control conductors C2|8 and Ci52,whereby the trunk circuit 40 is marked against seizure over the trunksection |49 by one of the connector switches provided in the C. A. X I0.At its contacts 25|, the relay R250 opens a point in the operatingcircuit for the switching relay R240.

When the finder switch 25 of the assigned link |5 operates to extend theconnection from the trunk section |50 to the connector switch 30, thecontrol relays of the connector switch operate momentarily to impressground potential upon the positive talking conductor C|53, thereby tocause the energization of the cut-off relay R220 over a circuitincluding this talking conductor and the contacts 222 and 224.Coincident, with the energization of the relay R220, ground potential isimpressed upon the control conductor CI 54 by the control relays of theconnector switch 30, whereby the trunk circuit 45 is marked againstseizure by another of the connector switches. The cut-off relay R220,upon operating, locks to the grounded control conductor C| 55 over apath including the contacts 223, 236 and 240. relay R220 opens itscontacts 224 to interrupt its operating circuit. At its contacts 22| and225, the relay R220 disconnects the windings of the line relay R2 I0from the conductors of the trunk 9|. At its contacts 222, the relay R220extends the calling loop circuit to the connector portion of the link.At its contacts 220, the relay R220 completes an obvious operatingcircuit for the slow-acting lockout relay R200. At its contacts 221, therelay R220 opens a point in the operating circuit for the supervisoryrelay R230. 'Ihe line relay R2l0, upon restoring in response tooperation of the cut-off relay R220, opens its contacts 2|3 and 2|4included in the start circuits extending to the common equipment 20,whereby the operated relays of this equipment are deenergized andrestore to condition the common equipment for use in handling anothercall. At its contacts 2|2, the relay R2|0 prepares the operating circuitfor the relay R230. The lockout relay R200, upon operating, opens itscontacts 204 and 205 further to interrupt the start circuits extendingto the common equipment 20. At its contacts 203, the relay R200 opensanother point in the operating circuit for the supervisory relay R230.At its contacts 202, the relay R200 prepares an alternative path forimpressing ground potential upon the control conductor C|55. At itscontacts 20|, the relay R200 prepares a locking circuit for itself, andcompletes a locking circuit for the guard control relay R250, the lattercircuit extending from ground by way of the contacts 226 and 20|, andthe winding of R250 to battery.

After this locking circuit is completed, the

After the connection has been extended through the trunk circuit 45 tothe connector switch 30, it may be forwarded to the substation A, forexample, served by the line in the exact manner described above withreference to the call routed through the trunk circuit 40. Supervisionof the call is under the control of the backbridge relay embodied in theconnector switch 30, this relay being arranged to follow the connectionrelease and call answering operations performed at the called substationA to transmit corresponding supervisory signals to the position ci theoperator handling the call at the operators switchboard 6 in the centralexchange 5. The release of the connection is also accomplished in amanner similar to that described above with reference to the trunkcircuit 40. Thus, when the operator receives a disconnect signal andwithdraws the calling plug of the cord circuit included in theconnection from the plug terminating the conductors of the trunk 9|, theoperated relays of the link |5 are caused to rele-ase, the line circuitI2 is released, and the link |5 is marked as idle in the distributorrelays of the common equipment 20. During the release of the link l5,ground potential is removed from the control conductor C|55 to cause thedeenergization and release of the cut-01T relay R220. 'Ihis relay, uponrestoring, opens the operating circuit for the lockout relay R200, andthe locking circuit for the guard control relay R250. When the twolast-mentioned relays restore, the trunk circuit 45 is fully released,and both this circuit and the trunk circuit 40 are marked as idle.

The manner in which the four relays R220, R2| 0, R200 and R250 cooperateto lock the trunk 9| and the two trunk circuits 40 and 45 out of servicewhen a permanent calling condition is present on the trunk 9| issubstantially similar to the mode of operation of the relays R|20, Rl I0and R|00 to accomplish this end, and will be clearly apparent from Itheforegoing explanation of the operation of the three latter relays tolock to the trunk 02 and the trunk circuit 40 out of service when apermanent calling condition exists on the trunk 02.

As indicated above, the toll trunks 0| and 02 may be used for routingtoll calls from the substations served by the C. A. X |0 to the tolloperators position provided at the switchboard 6 in the central exchange5. If desired, provisions may be made whereby these toll trunks areuse-d in handling C. A. X subscriber calls to the central exchangesubscribers when the calls are initiated at substations servingsubscribers who pay only for local exchange service and are to becharged for central office calls. In such case, the other C. A. Xsubscribers, namely, those paying a higher rate for both local andcentral exchange service, are permitted to have access to the freeservice trunks and to the combination toll and free service trunk 9|.

Assuming that a call initiated at the substation A is to be routed tothe toll operators position at the switchboard 6 and, further, that thelink I5 is assigned to the use of the call, the calling subscriber,after initiating the call in the usual manner to cause the seizure ofthe line by the finder switch 25, dials the four digits necessary tocause the connector switch 30 to seize the trunk section |49 terminatingat the contact set having the 02 directory number designation. It willbe understood that if the rst trunk 0| is idle, the trunk circuit 35 isseized, and the trunk 0| is utilized in forwarding the On the otherhand, if the toll trunkthe call is initiated, the trunk preselectYrelays 50 1 f occupy a position such that the connector switch 30automatically seizes the trunk circuit 40. Incident to the seizure` ofthis trunk circuit, the control equipment of the connector switch 30functions to complete a loop circuit between the connector switch 30 andthe trunk circuit 40, and to impress ground potential upon the controlconductor CI52.v When the conductor CI52 is connected to ground, therelay RIB is energized over a circuit including this conductor, thestrapped terminals I|8 and II'I, and the contacts |21, |03 and I|2. Uponoperating, the relay R|3IJ locks to the grounded control conductor CI52over a path including its contacts |36, "and opens, at its contacts |35,a point in the above-traced locking circuit for the cut-off relayVRI20.'l `At its contacts |33, the relay RI3|J completes an obviouscircuit for energizing the lower winding of the cut-off relay RI20. Therelay RI2Il, upon operating, completes the operating circuit for thelockout relay Rl, disconnects the windings of the line relay RIIOfrom-the conductors of the trunk 02, and connects the trunk conductor CII to the talking conductor CI5I of the trunk section |49.` In thisregard it will be apparent that when the relay RISIl operates, itprepares, at its contacts |3I, |32, |34 and |31, paths for reverselyconnecting the conductors Cl |5 and CIIISY to the conductors Cl5 andCI5I, whereby an orf-hook supervisory signal is produced at the tolloperators position of the switchboard 6 when the call is answered.

'Ihe lockout relay RIGD, upon operating, opens its contacts |03 tointerrupt the above-traced operating circuit for the relay R|30. At itscontacts |04 and |05, the relay RIDD further opens the start circuitsextending to the common equipment 20. At its contacts IGI, the relay R|00 prepares its locking circuit, and, at its contacts |02, prepares oneof the previously traced paths for impressing ground potential upon thecontrol conductor CI52. Following the operation of the relay RIIJU, nofurther operation of the relay equipment embodied in the trunk circuit40 occurs, until the connection is released at the calling substation A.After the relay RI operates reversely to connect the talking conductorsof the trunk 02 to the talking conductors of the trung section |49, theringing control equipment converse with the calling subscriber at thesub-J station A to ascertain the identity of the desired substation orparty, and may forward the'connection to the desired substation in amanner well understood in the art.

The release of the connection extending between the substation A and thetoll operators position at the switchboard 6, is entirely under thecontrol of the calling subscriber. Thus, when the connectionis releasedat the substation A, the line circuit I2 and the link lI5 are caused.V

to release. in the manner briey vdescribed labove l 'l and pointedoutwithlparticularity in the previ-1"*- ously referred to copending.application; During-Hy the-release of the link |5,groundpotential-is relmoved from the control conductor CI52 to cause I- the deenergizationofthe relay-RI30.f1 Thisrelay,

upon restoring its contactsy |3I', |32, |34 and-|31- to normal,reversesthe directionof current flow over the conductors -of the trunk v02,3 whereby: the r usual disconnect signal is producedfby ythesuper- Avisoryfsignal lamp associated with this vtrunk-at the toll operatorsposition of therswitchboardl-G. f-

In releasing, the relay RI30 also opens the operf ating circuit for? therelay RI 23.5 The relay.' RI20 `Isf- 'now restores lto bridgethewindings of the line: relay RI I0 across the conductors of thetrunk.|l2.i1

In the event the connection hasnot beencleared out at the tolloperatorsposition-of ythe switchboard 6 prior:` to the release of theconnection.: at the substation A, the `conductors of the trunk" 02areconnectedltogether overA a direct currenti.l

path extending through the operators `cord lcir-1'` cuit in use at thetoll operators position. 1Ac' cordingly, the line relay RI II) isenergized when its windings .arebridged across theconductors of thetrunk02,"and operates to complete the= f locking circuit for the lockoutrelay RIOI'L The' `v two relays RI I0 and R-Il are thus held operateduntil theconnection is cleared out at the toll operators position of theswitchboard 6.

With

these two relays operated and :the -two relays R|20 and RISI) restored,the previously traced path including the contacts |02 and |21 iscompleted for impressing ground potential uponthe f Vcontrol conductorCI52, thereby to guard the'.l

hand, the connection is cleared out at the tollI operators position ofthe switchboard 6 prior kto l its release at the calling substation A,the line relay RI I0 is not energized in response to the -re lease ofthe cut-oi relay `IRIZI).` Accordingly;

the three relays R|30,.R|20 andvRI sequen- Y tiallyrestore in the ordernamed and .in a manner clearly apparent from the Iabove explanation whenthe control equipment of the link I5 functions to disconnect the controlconductor CI52 from ground.

Assuming that the trunk circuit 40 is used in conjunction with the trunkcircuit 45 to terminate the combination toll and freeservice trunk9I,the relay operations -which occur incident to the extension ofthe'above-described call to the trunk circuit 40, are substantially thesame as describedabove. howeventhe switching relay R240 is energized linparallel with the supervisory relay R|3 when i With the latterarrangement,

the control equipment of the connectorv switchv 30 operates to impressground potential upon the control conductor CI52. vThe circuit forenergizing these two relays in parallel extends by way of the groundedconductor CI52 and the contacts 25| to theconductor C2|1 where itdivides, one' branch extending through the winding of R240 to battery,and the other branch extending by way of the contacts |21, |03 and |I2,and the winding of RISO to battery. The relay R240, upon operating,opens its contacts 242 and 244 to disconnect the conductors of the trunk9| frornthe .trunk circuit 45, and closes its contacts 24| and L,

243 to connect these conductors to the conductors C2|5 and C2|5 whichextend to the trunk circuit 40. Accordingly, the ringing current whichis transmitted by the connector switch 30 over the trunk section |09following seizure of the trunk circuit 00, is projected over the trunk9| to energize the incoming call signal device provided in associationwith this trunk at the op eratcrs switchboard in the central exchange 5.At its contacts 242, the relay R240 opens a point in the operatingcircuit for the relay R230.

At its contacts 265, the relay R220 completes an obvious path forimpressing ground potential upon the control conductor C|55, thereby toguard the trunk circuit 45 against seizure by the connector switches ofthe C. A. X l0. In handling a call of this character, the other relaysof the trunk circuit 40, namely, the relays R|00, Rl l0 and R|20 operatein the exact manner described above with reference to the call routed tothe toll operators position of the switchboard over the trunk 02. Itwill be observed that the switching relay R200 is held energized over acircuit including the connected control conductors C2i 1, C2|8 and C|52until the connection is cleared out at both the calling substation A andthe position of the operator handling the call at the switchboard 6 inthe central exchange 5.

Since the trunk 0| is primarily provided for free service calls tothecentral exchange subscribers, it will normally be seized by theconnector switches of the C. A. X l0 through the trunk circuit 45.Assuming, for example, that the above-described call originating at thesubstation A is routed through the finder-connector link l to th-e trunkcircuit 45 at a time when the trunk 0| is idle, the connector switch 30,upon operating to its ringing position, impresses ground potential uponthe control conductor Ci 55 of the trunk section |56 to energize thesupervisory relay R230 over a circuit including this control conductorand the contacts 246, 22T, 203 and 212. Upon operating, the relay R230completes an obvious circuit for energizing the lower winding of thecut-off relay R220, and locks to the grounded control conductor Ci55over a path including its contacts 231 and the contacts 24%. At thecontacts 222, 23|, 232, 23d and 235, the two relays R220 and R230, inoperating, reversely connect the conductors of the trunk 9| to thetalking conductors C153 and C|54 of the trunk section |56, whereby theproper ofi-hook supervisory signal is produced by the signal lampassociated with the trunk 9i after the call is answered at the operatorsposition of the switchboard 6 at which the trunk 0| is terminated. Inoperating, the relay R220 also opens its contacts 22| and 225 todisconnect the windings of the line relay R2|0 from the conductors ofthe trunk 0|. At its contacts 221, the relay R220 opens a point in theabove-traced operating circuit for the supervisory relay R230. At itscontacts 222, the relay R220 completes an obvious circuit for energizingthe lockout relay R200. The relay R200, upon operating, closes itscontacts 20| to prepare the previously described locking circuit foritself, and to complete the previously traced operating circuit for theguard control relay R250. At its contacts 202, the relay R200 preparesan alternative path for impressing ground potential upon the controlconductor C|55. At its contacts 203, the relay R200 opens another pointin the operating circuit for the supervisory relay R230. At its contacts204 and 205, the relay R200 opens further points in the start circuitsindividual to the trunk circuit and extending to the common equipment20. The guard control relay R250, upon operating, closes its 'contacts252 to impress ground potential upon the control conductor C|52 and thusguard the trunk circuit 40 against seizure for the duration of the call.At its contacts 25|, the relay R250 opens a point in the previouslytraced circuit for energizing the relays R240 and R|30 in parallel.

After the call, as routed through the trunk circuit 45 and over thetrunk 4| to the operators switchboard 6, is answered at the position ofthe operator where this trunk is terminated, the answering operator mayconverse with the calling subscriber and ascertain the identity of theparty desired or the directory number of the substation desired, and mayextend the connection to the desired substation in a manner wellunderstood in the art.

The release of the finder-connector link I5 is in this case alsoentirely under the control of the calling subscriber at the substationA. During the release of this link, which occurs when the callingsubscriber restores the receiver provided at the substation A to itssupporting hook or cradle, the control conductor C 55 is disconnectedfrom ground in the connector switch 30, thereby to deenergize thesupervisory relay R230. Upon restoring, the relay R230, at its contacts23|, 232, 234 and 235 reverses the direction of current flow over thetrunk 3|, whereby a disconnect signal is produced at the position of theoperator handling the call in the central exchange 5. Upon restoring,the relay R230 also opens its contacts 233 to deenergize the cut-offrelay R220. In the event the connection has not previously been clearedout at the position of the operator handling the call in the centralexchange 5, the cutoff relay R220, upon restoring, completes theoperating circuit for the line relay R2 i0. The relay RZiii, uponoperating, closes its contacts 2|| to complete the locking circuits forthe guard control relay R250 and the lockout relay R200. Thus, the threerelays R2|0, R200 and R250 are held operated until the connection iscleared out at the position of the operator handling the call in thecentral exchange 5. With the lockout relay R200 operated, and thecut-off relay R220 in its restored position, the control conductor C|55is connected to ground over a path including the contacts 200, 221 and202. Thus, the trunk circuit 5 is guarded against seizure by theconnector switches of the C. A. X I0. With the guard control relay R250operated, ground potential is also impressed upon the control conductorC|52 over a path including the contacts 252 to guard the trunk circuit40 against seizure. When the connection is cleared out at the positionof the operator handling the call in the central exchange 5, the linerelay R2i0 is deenergized and restores in the manner previouslyexplained. This relay, upon restoring, causes the sequential release ofthe relays R250 and R220 in an obvious manner. Thus, the trunk circuit45 is fully restored to normal, and the two trunk circuits 40 and 45 aremarked as idle. In the event the connection is cleared out at theposition of the operator handling the call in the central exchange 5prior to the release of the connection at the calling substation A, therelays R230, R220, R250 and R200 are caused sequentially to restore inthe order named and in a manner clearly apparent from the aboveexplanation. iihen these relays restore, the trunk circuit 45 is fullyreleased and both'thisV circuitfand the trunk circuit i4!) are marked asidle.

While there has been described whatfis at pres-v ent considered to bethe preferred-.embodiment of the invention, it will befunderstood thatvarious-modications may be made'` therein,l and vit is contemplated tocover in the appended claims all-such modifications as fall within thetrueconnected `and being arranged in sets for subscriber linetermination, a pairof trunk circuits respectively including trunksections terminated at sets of said outlet contacts having different`directory number designations, a second exchange, a trunk extending fromsaid second exchange to said trunk circuits, and means controllablethrough said connector switches for selectively connecting said trunk toone or the other of said trunk circuits.

2. In a telephone system, an exchange includingl automatic finder andconnector switches for setting up connections between the lines of thesystem,- the corresponding outlet contacts of said iinder and connectorswitches being conductively connected and being arranged in sets forsubscriber line termination, a pair of trunk circuits respectivelyincluding trunk sections terminated at =-s'ets of said outlet contactshaving different director number designations, a second exchange, atrunk extending from said second exchange` to said trunk circuits, andmeans comprising a relay controlled over a circuit including one of thecontacts of one of said pair of contact sets for selectively connectingsaid trunk to one or the other of said trunk circuits.

3. In a telephone system, an exchange including vautomatic nder andconnector switches for setting up connections between the lines of thesystem, the corresponding outlet contacts of said finder and connectorswitches being conductively connected and being arranged in sets forsubscriber line termination, a pairoi trunk circuits respectivelyincluding trunk sections terminated at -sets ofsaid outlet contactshaving diierent directory number designations, a second exchange, atrunk normally connected to one of said trunk circuits and extending tosaid second exchange, and switching means operative to disconnect saidtrunk from said one trunk circuit and to connect said trunk to the otherof said tru'nk'circuits.

4. In a telephone system, an exchange including automatic finder andconnector switches for setting up connections between the lines of thesystem, the corresponding' outlet contacts of said nderand connectorswitches being eonductively connected and being arranged in sets forsubscriberline termination, a pair of trunk circuits respectivelyincluding trunk sections terminated at sets of said outlet contactshaving different directory number designations, a second exchange, atrunk normally connected to one of said trunk circuits and extending tosaid second exchange, and means comprising a relay controlled over acircuit including one of the contacts of the contact set terminating thetrunk section of the other of said trunk circuits for disconnecting saidtrunk from said one trunk circuit and .for connectingfsaid trunk to theother of said trunk circuits.

5. In a telephone system, an exchange. including automatic finder andconnector switches for set ting up connections between the lines or thesyscircuits, means controlled over the control conductor of one of saidtrunk sections for selectively connecting said trunk to said trunkcircuits, and means controlled over the control conductors of said trunksections for marking both of said trunkcircuits busy when either trunkcircuit is occupiedw vl with a call.l

6. In -a telephone system, an exchange including 1;.' :automatic finderand connectorswitches for setting up connections between the lines ofthe system, the corresponding outlet 'contacts of said finder andconnector switches being conductively connected and said contacts beingarranged in a control contact, a pair of trunk circuits respectivelyincluding trunk sections terminated at setswv of said outlet contactshaving different directory 1 number designations, each of said trunksectionsY including 'a pair of talking conductors and a controlconductor, a second exchange, a trunk extending from said secondexchange to said trunk circuits, means .controlled over the controlconductor of one of said trunk sections for selectivelyz f'connectingsaid trunk to said trunk circuits, and

means responsive to the seizure or either of saidf trunk circuits by oneof said connector switches for reversely connecting the talkingconductors-ffof said trunk to the talking vconductors of the v' trunksection individual to the seizedtrunk cir-l l cuit.

'7. In a telephone system, an exchange including automatic finder andconnector switches for setting up connections between the lines of thesysif litem, the corresponding outlet contacts of lsaid nder andconnector switches being conductively connected and said lcontacts beingarranged in sets each including a pair of talking contacts and a controlcontact, a ipair of trunk circuits respec-' ,tively including trunksections terminated at sets of said outlet contacts having diierentdirectory number designations, each of said trunk sections f including apair of talking conductors and a'control conductor, a second exchange, atrunk extend-l A .ling fromisaid second exchange to said trunk cir-.-

cuits, means controlled over' the control conductor o" of one orf saidtrunk sections for selectively con-I' y necting said trunk to said trunkcircuits, "and means individual to said trunk circuits and lcon-mntrolled over the control conductors of the associated trunk sections forreversely connecting the talking conductors of said trunk to thetalkingv`l`- conductors off the respective associated trunk sections.

8. In a telephone system, an exchange including automatic nder yandconnector switches for setting up connections betweenlthe lines of thesystern, the corresponding outlet contacts of said" r nder and connectorswitches being conductivelyf f lconnected and' said contacts beingarranged in sets each including a pair of talking contacts and .f

sets each including a pair of talking contacts and a control contact, apair of trunk circuits respectively including trunk sections terminatedat sets of said outlet contacts having dierent directory numberdesignations, each of said trunk sections including a pair of talkingconductors and a control conductor, a second exchange, a trunk extendingfrom said second exchange to said trunk circuits, means icontrolled overthe control conductor of one of said trunk sections for selectivelyconnecting said trunk to said trunk circuits, means controlled over thecontrol conductors of said trunk sections for marking both of said trunkcircuits busy when either trunk circuit is occupied with a call, andmeans responsive to the seizure of either of said trunk circuits by oneof said connector switches for reversely connecting the talkingyconductors of said trunk to the talking conductors of the trunk sectionindividual to the seized trunk circuit.

9. In la telephone system, an exchange including automatic finder andconnector switches for setting up connections between the lines of thesystem, the corresponding outlet contacts of said nder and connectorswitches being conductively connected and said contacts being arrangedin sets each including a pair of talking contacts and a control contact,a pair of trunk circuits respectively including trunk sectionsterminated at sets of said outlet :contacts having different directorynumber designations, each of said trunk sections including a pair oftalking conductors and a control conductor, a second exchange, a trunkextending rom said second exchange to said trunk circuits, meanscontrolled over the control conductor of one of said trunk sections forselectively .connecting said trunk to said trunk circuits, meanscontrolled over the control conductors of said trunk sections formarking both of said trunk circuits busy when either trunk circuit isoccupied with a call, and means individual to said trunk circuits andcontrolled over the control conductors of the associated trunk sectionsfor reversely connecting the talking conductors of said trunk to thetalking conductors of the respective associated trunk sections.

10. In a telephone system, an exchange including automatic finder andconnector switches for setting up connections between the lines of thesystem, the outlet contacts of said switches being arranged in sets eachincluding a control contact and a pair of talking contacts, multipleconductors providing unbroken connections between the correspondingtalking and control contacts of said contact sets, a trunk circuitcomprising a trunk section including talking and control conductorsterminating at the control and talking multiple conductorsinterconnecting the contacts of the contact sets having a predetermineddirectory number designation, a second exchange, a trunk interconnectingsaid trunk circuit and .said second exchange, and means in said trunkcircuit controllable over said trunk section for transmittingsupervisory signals over said trunk.

11. In a telephone system, an exchange including automatic finder andconnector switches for setting up connections between the lines of thesystem, the outlet contacts of said switches being arranged in sets eachincluding a control contact and a pair of talking contacts, multipleccnductors providing unbroken connections between the correspondingtalking and control contacts of said contact sets, a trunk circuitcomprising a trunk section including talking and control conductorsterminating at the control and talking multiple conductorsinterconnecting the contacts of the contact sets having a predetermineddirectory number designation, a second exchange, a trunk interconnectingsaid trunk circuit and said second exchange, and means comprising asupervisory relay controllable over the control con- 7Vductor of saidtrunk section for transmitting supervisory signals over said trunk.

12. In a telephone system, an exchange including automatic nder andconnector switches for setting up connections between the lines oi thesystem, the outlet contacts of said switches being arranged in sets eachincluding a control contact and a pair of talking contacts, multipleconductors providing unbroken connections between the correspondingtalking and control contacts of said contact sets, a trunk circuitcomprising a trunk section including talking and control conductorsterminating at the control and talking multiple conductorsinterconnecting the contacts of the contact sets having a predetermineddirectory number designation, a second exchange, a trunk interconnectingsaid trunk circuit and said second exchange, and means comprisingcoacting line and lockout relays included in said trunk circuit forlocking said trunk and said trunk circuit out of service when apermanent calling condition exists on said trunk.

13. In a telephone system, an exchange including a plurality ofnder-connector links for setting up connections between the lines of thesystem, equipment common to said links and including finder startcircuits, the outlet contacts of the finder and connector portions ofsaid links being arranged in sets each including a control contact and apair of talking contacts for subscriber line termination, multipleconductors providing unbroken connections between the correspondingtalking and control contacts of said contact sets, a trunk circuitcomprising a trunk section including` talking and control conductorsterminating at the control and talking multiple conductorsinterconnecting the contacts of the contact sets having a predetermineddirectory number designation, a trunk extending to said trunk circuit,and means comprising line and cut-0E relays included in said trunkcircuit and respectively controlled over said trunk and said trunksection for controlling said inder start circuits.

14. In a telephone system, an exchange including a plurality oflnder-connector links for setting up connections between the lines ofthe system, equipment common to said links and including finder startcircuits, the outlet contacts of the Iinder and connector portions ofsaid links being arranged in sets each including a control contact and apair of talking contacts for subscriber line termination, multipleconductors providing unbroken connections between the correspondingtalking and control contacts of said contact sets, a trunk circuitcomprising a trunk section including talking and control conductorsterminating at the control and talking multiple conductorsinterconnecting the contacts of the contact sets having a predetermineddirectory number designation, a trunk extending to said trunk circuit,means comprising line and cut-off relays included in said trunk circuitand respectively controlled over said trunk and said trunk section forcontrolling said finder start circuits, and meansr comprising a lockoutrelay coacting with said line relay for locking said trunk circuit andsaid trunk out of service when a permanent calling condition exists onsaid trunk.

terminating at lthe control and talking multiple conductorsinterconnecting the contacts .of the Contact 'sets having apredetermined directory number designation, a trunk extending to s'aidtrunk circuit, means comprising line and .cut-'onf relays included insaid trunk circuit and respeta tively controlled over said trunk andsaid trunk section for controlling said finder start circuits, and meanscomprising a supervisory relay 'con'- trollable over said trunk sectionfor transmitting supervisory signals over said trunk.

JOHN H. VOSS.

